The present disclosure is directed to temperature data acquisition on process tubes in a furnace.
A steam methane reformer is an example of a furnace containing a plurality of process tubes. One type of furnace for steam methane reforming can utilize numerous process tubes (including one configuration that has more than 400 process tubes) containing a catalyst (for example, a reforming catalyst) for transporting a process fluid (for example, steam and a hydrocarbon) and reacting the process fluid therein. The furnace, in one example, can include vertically extending process tubes positioned in parallel rows with about 30 to 60 tubes in each row. The distance between two rows of tubes is about 2 to 3 meters. The tubes can extend vertically about 12 meters and have an outer diameter of 100 to 150 millimeters. The tubes can be positioned in the row with a center-to-center spacing of 250 to 500 mm. About 10 to 20 burners can be positioned between each set of two rows of tubes. A total of eight or more rows of tubes and nine or more rows of burners can be included in the furnace.
Generally, energy efficiency for industrial processes, such as steam methane reforming, is becoming more important. For many processes, the efficiency of the process is related to the ability to monitor/maintain certain temperatures of the process tubes. More precise monitoring of the temperature of the process tubes can permit improved energy efficiency by permitting more accurate data to be used for process control.
One way to improve the efficiency of a furnace is to maintain uniform temperatures among the process tubes at a predetermined elevation in the furnace. Thus, the measuring or monitoring of the temperature of each of the process tubes at a predetermined location or elevation can be needed to obtain the desired efficiency improvement. In addition, the process tubes of a furnace can be under very high internal pressures (up to about 50 atmospheres) and at very high temperatures (up to about 950° C.). Thus, a slight change in temperature can reduce the operational life of a process tube. For example, operating at about 10° C. above the design temperature for the tube can reduce the operational life of the tube by as much as one half. The cost of repairing and/or replacing the tubes can be high due to the use of special alloys in the tubes that are needed to permit the tubes to survive the operational conditions of the furnace. In addition, the loss of production due to repairing the tubes results in lost revenue. As such, furnace operators also measure/monitor the tube temperatures to avoid exceeding the tube design temperature in addition to trying to obtain efficiency improvements.
In one method of measuring/monitoring the temperature of process tubes, an operator may use an optical pyrometer. When using the optical pyrometer, the operator aims the device at a predetermined location on a process tube and then activates the device. Upon activation, the optical pyrometer measures thermal radiation and displays or records a corresponding temperature for the predetermined location on the process tube and the operator logs the measured temperature for each tube. The operator repeats the process for each of the tubes. The use of the optical pyrometer has several drawbacks in that high temperature exposure may occur, the same predetermined location may not be used for all tubes, the temperature of a selected tube may not be measured, the same tube may be inadvertently measured twice instead of the desired adjacent tube, and the process may take too long resulting in temperature fluctuations for the tubes.
More recently, thermal imaging devices have been implemented to measure/monitor the temperature of the process tubes. An example of a thermal imaging device and method is described in U.S. Pat. No. 8,300,880 B2, incorporated herein by reference. In U.S. Pat. No. 8,300,880 B2, a single imaging device is moved from viewport to viewport to collect a plurality of images and temperature information is obtained for most or all of the process tubes. This approach has the advantage of being able to obtain temperature information for all of the process tubes but the disadvantage of requiring the operator to move the imaging device from viewport to viewport.
A thermal imaging device suitable for obtaining temperature information of process tubes is described in U.S. patent application Ser. No. 14/963,644, incorporated herein by reference. In U.S. patent application Ser. No. 14/963,644, an imaging device that can be fixed to the viewport door is disclosed. Multiple imaging devices, each mounted to a different viewport door, can be used to obtain temperature information for most or all of the process tubes in the furnace. This approach has the advantage of being able to obtain temperature information for all of the process tubes without requiring the operator to move the imaging device from viewport to viewport. This approach also has the advantage of being capable of providing repeated periodic temperature measurements in a somewhat continuous manner. This approach has the disadvantage of requiring many thermal imaging devices, which may be expensive.
Industry desires to obtain temperature information for a plurality of process tubes in a furnace without requiring an operator to move from viewport to viewport to capture the temperature information.
Industry desires to determine temperature information for a plurality of process tubes in a furnace with a reduced number of fixed thermal imaging devices, i.e. without requiring a full complement thermal imaging devices where each and every process tube is thermally imaged.
Industry desires repeated periodic temperature measurements for process control.